Of course not everyone with an allergy or allergic reaction needs an Epipen.
But it is common practise in the UK by NHS clinicians to prescribe them to people who have had an anaphylactic reaction.
http://www.redbridgeccg.nhs.uk/downl...nes%202014.pdf
Without knowing the details of someone's case it is not possible to say why the CAA has decided that they cannot hold a Class 1.